1. Technical Field of the Invention
This invention relates to an optical information recording medium for writing or reading an information upon irradiating a high energy flux density beam such as a laser beam and, more particularly, to an optical information recording medium comprising a recording layer mainly made of fine copper particles dispersed in a hydrophilic colloid.
2. Description of the Prior Art
There have so far been known the recording layers comprising various types of compositions, in the optical information recording media usable in such a manner that an information such as a sound, image, or the like is optically recorded according to the variations of the configuration, dimensions or the like of a pit or block, or that an information is optically picked up and is then converted into a sound signal or an image signal so as to reproduce it. They may include, as one of the examples thereof, a thin film recording layer comprising a metalloid such as tellurium, bismuth, selenium or the like and the oxides thereof (Yamashita et al., The 28th Applied Physics Lecture Proceedings, 1981, p. 141) and a chalcogen compound such as selenium-tellurium-arsenic (M. Terace et al., P. Appl. Phys. No. 50, 1979, p. 6881), tellurim-arsenic or the like. They can, however, hardly be mass-produced continually, because a vacuum equipment has to be used in a manufacturing process, and they are disadvantageous because a relative reproduction error of a recorded information is increased by the deterioration, such as oxidation of the compounds being contained in a recording layer, and there are many toxic compounds among the compounds used, so that the safety thereof is not reliable.
Optical information recording media capable of solving these disadvantages include, as disclosed in Japanese Patent Publication Open to Public Inspection (hereinafter called Japanese Patent O.P.I. Publication) Nos. 12425/1982, 24290/1982 and 39989/1982, those having a recording layer comprising a binder into which a metal is dispersed in the form of fine particles of not larger than 50 nm in the average size. This type of recording media each have a recording layer comprising black fine particles dispersed therein, and are used for recording upon increasing the reflectivity of the recording layer by irradiating it with laser beams. Accordingly, as compared with another type of recording media being used for recording by lowering the reflectivity of the recording layer, they have a disadvantage that a tracking signal is hardly obtained.
Recording media being used in the systems in which a recording is carried out by lowering the reflectivity of the recording layer thereof further include, for example, that disclosed in Japanese Patent O.P.I. Publication No. 10491/1981. This medium has a recording layer containing a binder comprising a polymer in which fine particles of a metal or the oxide thereof are dispersed; and the particle size of the metal or the oxide thereof is 20 to 150.ANG.. This medium is, however, manufactured by making use of a toxic organic solvent to form fine particles from a metal carbonyl as an initial raw-material. It is, therefore, disadvantageous in that not only the manufacturing environment will cause a problem, but also the fine particles will be unstable and rapidly oxidized and the recording layer will become uneven in the direction of thickness. In addition, the binder, which is a dispersion medium for the fine particles of a metal or the oxide thereof, is a lipophilic polymer, therefore, the so-called aqueous coating is not possible and the manufacturing environment becomes undesired from the viewpoint of health conditions. Further, the reflectivity of this recording medium is as low as not higher than 30%, therefore, it is not suitable for a reflecting light reading type optical information recording medium.
Recording media being used by lowering the reflectivity of the recording layer thereof include, for example, those disclosed in Japanese Patent O.P.I. Publication Nos. 108995/1980, 33995/1981, 49296/1981 and 49297/1981. This type of recording media comprises a support bearing thereon a silver halide emulsion layer and a recording layer of which the reflective silver particles are deposited, by a photographic chemical development and physical development, in the neighborhood of the surface of the silver halide emulsion layer. These media may be regarded as the highly sensitive optical information recording media from the viewpoint of that they contain a thermally insulating gelatin superior to silver. In these recording media, however, the recording layer thereof is 3 to 6 .mu.m in thickness, therefore not only the sensitivity has its limit but also the silver density has its gradient distribution in the direction of thickness, and only the neighborhood of the recording layer surface becomes highly reflective. Accordingly, this type of recording media is hardly applied to the systems in which a recording or reproducing is carried out through a support.
On the other hand, in the publication having disclosed the above-mentioned prior art, there are only the descriptions mainly of such a recording medium of which the surface of the recording layer provided onto the support is made reflective. These media each are required to be provided with such a protective layer as a silicon oxide layer or a polymethylmethacrylate layer, or the whole of the recording medium is encapsulated so that the pits on the recording layer's surface may be protected against dusts. Accordingly, a protective layer coating process, a medium encapsulating process or the like is required.
To avoid such a trouble as described above, a recording medium having a transparent support made of polymethylmethacrylate, glass-plate or the like is ordinarily used to record therethrough and in this case, it has been known that transparent supports each are superposed on the both sides of the recording medium.
The inventors have attained this invention by finding out the facts that an optical information recording medium having a recording layer comprising a hydrophilic colloid containing fine particles consisting essentially of copper is very inexpensive in cost as compared with those using silver, gold, palladium, cobalt, nickel or the like; and it is preferred from the viewpoint of health condition in a working environment because it is less toxic enough as compared with those using mercury or lead; and, in addition, it is high in sensitivity and excellent in stability.
As the recording materials in which copper is utilized, there have so far been known those each having a light-sensitive image-forming emulsion layer comprising particles of a cuprous halide dispersed in a macromolecular substance. For example, there have been disclosed, in the literature, Poznan Towarz Przyjacio Nauk. Prace Komisji Mat. Przyrod, 7, p. 23, 1956, an emulsion layer comprising the pulverized crystals of CuCl dispersed in an aqueous gelatin solution of 10% concentration, and in West German Pat. No. 950428 an emulsion layer comprising cuprous bromide produced through a reaction of cupric bromide (CuBr.sub.2) with sulfurous acid gas (SO.sub.2) or hydrogen sulfide (H.sub.2 S) and dispersed in polyvinyl alcohol. These emulsion layers are effective, in general, as a light-sensitive photographic element, however, they may not be put in practical use as an element of an optical information recording medium because they have a problem of the graininess thereof after a development. To be more concrete, the developed copper particles thereof are large in size and the distribution of the dispersed particles is uneven, and noises are thereby caused very seriously.